The process of channeling solar radiation to produce electric power is often accomplished through the use of heliostats, instruments consisting of one or more mirrors mounted on an axis which are moved by computerized clockwork to steadily reflect solar radiation in a predetermined direction (heliostat=sun's reflection in a constant direction). An example of a heliostat with two mirrors is shown in FIG. 1.
The mirrors on heliostats or dishes which are used to focus the solar radiation, known as "reflectors," may be many meters in diameter and are constantly exposed to the environment. As a result, over a period of time, the surface of reflectors is degraded by this exposure, and the reflector is no longer useful. At this time, the surface of the reflector or the reflector itself must be replaced.
Known methods for protecting the reflector surface from the environment include the use of laminated glass reflectors and plastic reflectors. Laminated glass reflectors include a reflective metal layer sandwiched between two glass sheets. These reflectors have a life span of approximately thirty years. They are scratch-resistant and therefore may be cleaned using ordinary soap and water. The glass layers are also impermeable to water and prevent water corrosion of the underlying reflective metal layer. However, glass reflectors are heavy and costly due to the increase in structural weight of the reflector, which is significant even when very thin glass is used. Glass is also vulnerable to hail and other impacts which result in exposure of the reflective metal layer. Glass is high in stiffness, and has a smaller coefficient of thermal expansion in comparison to the metal frame that supports the glass. Therefore, the glass must be applied as tiles of less than one square meter each.
Plastic (polymer film) reflectors include a layer of transparent plastic covering a reflective metal layer. Plastic reflectors are lighter, less expensive, and more flexible than glass reflectors. Layers of plastic can be adhered to metal substrates as a single sheet as wide as 1.5 meters and 10's of meters in length. Plastics have a higher coefficient of thermal expansion than metals, but their flexibility allows them to be bonded over large areas to metal support structures as a single piece. However, the plastic may be scratched during ordinary cleaning and therefore becomes dull over time. Furthermore, plastics are permeable and allow water to reach the underlying reflective metal layer, causing corrosion. As a result of these drawbacks, plastic reflectors have a life span of approximately seven to ten years.
A possible solution to the degradation problem of plastic reflectors is to remove the worn outer plastic layer and replace it with a new layer to lengthen the usable life of the reflector. However, the process of replacing the outer plastic layer is cumbersome, results in a coating that is inferior to the original coating, and is expensive to the point of being economically infeasible. For example, the replacement process often results in particles from the environment being trapped between the plastic sheet and the metal structure layer, thereby distorting the reflector. Also, the replacement sheet may not be properly tensioned and sealed to the reflective layer such that moisture may seep in and corrode the reflective metal layer.